Comparative analysis of early immune responses induced by two strains of Newcastle disease virus in chickens

Newcastle disease, caused by virulent strain of Newcastle disease virus (NDV), is an acute, highly contagious disease that is prevalent worldwide and is responsible for serious economic losses to the poultry industry. In the current study, we compared the early immune responses in chickens infected with two strains of velogenic NDV, a duck origin, named GD strain (Md/CH/LGD/1/2005, genotype VIId), and an chicken origin, F48E9 strain (genotype IX). The viral RNA level of GD strain was significantly higher than those of F48E9 in most tissues of chicken. Furthermore, the high level of viral RNA of the GD strain was associated with a stronger immune response compared to that of F48E9, characterized by upregulated expression of some of avian β‐defensins and cytokines, most of toll‐like receptors, and some of the other immune‐related genes investigated. This study thus demonstrated differences in host early immune responses to the two NDV strains. Further studies are needed to characterize the basic molecular mechanisms involved in the host responses in chickens infected by the two NDV strains. In this study, we showed that the GD NDV strain replicated more efficiently in most chicken tissues than the F48E9 strain. The higher levels of virus replication of the GD strain may be associated with a stronger innate immune response compared with the F48E9 strain.